229
FXUS65 KBYZ 181117
AFDBYZ
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BILLINGS MT
517 AM MDT TUE AUG 18 2026
KEY MESSAGES
- SCATTERED SHOWERS AND THUNDERSTORMS EXPECTED AGAIN TODAY. A FEW
STORMS COULD BE STRONG TO SEVERE.
- DRIER CONDITIONS WEDNESDAY AND THURSDAY.
- SEASONAL TEMPS IN THE 80S THROUGH MIDWEEK, PUSHING INTO THE
LOWER 90S BY LATE WEEK. INCREASING CHANCE OF PRECIPITATION
FRIDAY THROUGH THE WEEKEND.
UPDATE
HAVE MADE MINOR UPDATES TO THE FORECAST TO ACCOUNT FOR ONGOING
ISOLATED SHOWERS AND WEAK THUNDERSTORMS THIS MORNING, AS WELL AS
CONVECTIVE TRENDS THIS AFTERNOON. THE REST OF THE FORECAST REMAINS
ON TRACK. MATOS
SEE UPDATED AVIATION DISCUSSION BELOW
DISCUSSION
TODAY THROUGH MONDAY...
THE LINGERING SHOWERS AND STORMS AROUND NOW WILL GRADUALLY
DECREASE BY SUNRISE THIS MORNING. ANOTHER ROUND OF STORMS IS
FORECAST THIS AFTERNOON AND EVENING WHICH LOOKS SIMILAR TO THE
SETUP WE HAD LAST EVENING.
AS A VORT MAX PIVOTS THROUGH MONTANA MIDDAY TODAY STORMS WILL
KICK OFF OF THE MOUNTAINS OF SOUTH-CENTRAL MONTANA MID-TO LATE
AFTERNOON JUST AS THAT AREA OF BROAD SCALE ASCENT MOVES INTO THE
REGION. STORMS SHOULD BE ABLE TO INITIATE FAIRLY EASILY IN THIS
REGION OF CVA DUE TO THE ENHANCEMENT OF THE MOUNTAINS AS WELL AS
THE MINIMAL CIN DUE TO SUFFICIENT DAYTIME HEATING. CAPE VALUES
WILL BE VERY SIMILAR TO WHAT WE SAW MONDAY WITH WIDESPREAD
500-1000 J/KG. AS EVIDENT FROM LAST NIGHT'S STORMS, THIS WILL BE
PLENTY TO SUSTAIN STRONG STORMS. MID-LEVEL LAPSE RATES WERE A
TOUCH UNDER FORECAST YESTERDAY, SO TAKING THAT INTO ACCOUNT, I DO
EXPECT GOOD VALUES IN EXCESS OF 8 C/KM ACROSS THE CWA. MOISTURE
CONTENT ALSO SHOULD NOT CHANGE MUCH GOING INTO THIS EVENING. THE
THREATS TODAY WILL BE THE SAME AS YESTERDAY DUE TO THE STORMS
BEING DECENTLY HIGH BASED RESULTING IN A DOWNBURST / GUSTY WIND
THREAT. THE 0-6 KM SHEAR WAS ALSO UNDER FORECAST FOR MONDAY DUE IN
LARGE PART TO STRONGER 700-500MB WINDS HELPING TO TILT THE
STORMS. WHILE THE WINDS THROUGH THAT LAYER WILL NOT BE AS STRONG
AS YESTERDAY, THERE WILL STILL BE WIDESPREAD 30-40KTS OF SHEER
WHICH WILL BE PLENTY TO SUSTAIN SUPERCELLS. THE MAIN LIMITING
FACTOR IN TERMS OF HAIL DEVELOPMENT IS THE LACK OF CAPE AND HOW
SKINNY THE PROFILE IS. THAT BEING SAID, THE SHEAR IN THE HAIL
GROWTH ZONE IS VERY SUPPORTIVE OF TILTED STORMS AND HYDROMETER
SIZE SORTING. THIS WAS EXACTLY MY THINKING WHEN WRITING THIS
DISCUSSION 24 HOURS AGO AND IT APPEARS THAT A COUPLE STORMS WERE
ABLE TO SUPPORT GOLF BALL SIZED HAIL. THIS LENDS ITSELF TO THE
THEORY THAT STRONG SHEAR IS MORE IMPORTANT FOR HAIL DEVELOPMENT
THAN LARGE AMOUNTS OF CAPE. WHATEVER THE TRUE REASON IS, THE
ANALOG FROM MONDAY TO TUESDAY BEING VERY SIMILAR LEADS ME TO
BELIEVE THAT THERE COULD BE ANOTHER CONSIDERABLE SEVERE STORM THIS
EVENING WHEREVER IT IS ABLE TO TAKE ADVANTAGE OF THE MAXIMUM OF
ALL THESE INGREDIENTS.
WEDNESDAY WILL BE A TRANSITION DAY AS THE PARENT UPPER LEVEL LOW
MOVES OFF TO THE EAST. SHOWERS WILL PROBABLY BE HANGING AROUND THE
AREA WEDNESDAY MORNING AND QUICKLY DIMINISH / MOVE EAST BY MIDDAY.
BY WEDNESDAY NIGHT A RIDGE WILL BE IN PLACE OVER THE
INTERMOUNTAIN REGION WHICH WILL KEEP MOST OF THE CWA WARM AND DRY.
AS WEAK VORT MAXES RIDE ALONG THE RIDGE MID TO LATE WEEK, THERE
COULD BE WIDELY ISOLATED SHOWERS IN THE EASTERN 2/3 OF THE CWA ANY
GIVEN DAY. THIS PATTERN WILL CONTINUE INTO THE WEEKEND AS TEMPS
SLOWLY INCREASE EACH DAY. THERE IS STILL A DIFFERENCE BETWEEN THE
GFS AND ECMWF ENSEMBLES IN TERMS OF HIGHS FOR THIS WEEKEND AS THE
GFS WANTS TO HAVE US FLIRT WITH TRIPLE DIGITS AGAIN SATURDAY
WHEREAS THE ECMWF KEEPS HIGHS IN THE LOW 90S.
THE RIDGE SHOULD NOT STICK AROUND TOO LONG THOUGH AS MODELS HINT
AT IT ONLY LASTING INTO THE WEEKEND. THE POTENTIAL FOR A TROUGH TO
MOVE OFF OF THE BC COAST AND TRACK JUST NORTH OF THE
INTERNATIONAL BORDER IS POSSIBLE. THE TIMING OF THIS FEATURE STILL
VARIES GREATLY BETWEEN THE START AND THE END OF THE WEEKEND SO NO
CLEAR FORECAST CAN BE MADE AT THIS TIME. FOR ANYONE WHO IS
LOOKING FORWARD TO THE NEXT SEASON, THIS SEEMS TO HAVE A HINT OF
AN AUTUMN FLAVOR TO IT IN TERMS OF LOCATION AND PROGRESSION. WMR
AVIATION
11Z DISCUSSION...
ISOLATED SHOWERS AND A WEAK THUNDERSTORM OR TWO ARE LINGERING
OVER SOUTHERN MONTANA THIS MORNING. WIND GUSTS TO 40 MPH AND BRIEF
HEAVY RAIN ARE THE MAIN IMPACTS. ANY SHOWER/STORM WILL BE CAPABLE
OF REDUCING FLIGHT CONDITIONS TO MVFR/IFR. ADDITIONAL CONVECTION
IS EXPECTED THIS AFTERNOON AND EVENING, WITH DEVELOPMENT OVER AND
NEAR THE MOUNTAINS SOUTH (INCLUDING THE BIGHORNS) AND WEST OF
KBIL. LOOK FOR STORM DEVELOPMENT BY 20Z AND STORMS TO MOVE
EASTWARD THROUGH THE AFTERNOON. THE PRIMARY CONCERNS WITH
CONVECTION IN THE AFTERNOON ARE STRONG WIND GUSTS TO 50 KNOTS,
HAIL, AND HEAVY RAINFALL. MATOS
PRELIMINARY POINT TEMP/POPS
TDY WED THU FRI SAT SUN MON
-------------------------------------------------------
BIL 084 059/088 059/093 062/090 065/092 063/089 062/088
5/T 50/U 00/U 00/U 12/W 31/B 21/U
LVM 082 048/085 051/091 054/090 056/089 054/086 052/086
3/T 20/U 00/U 00/U 34/T 32/T 22/W
HDN 086 054/090 055/094 059/093 063/094 061/090 059/091
3/T 50/U 00/U 00/U 12/W 21/B 21/U
MLS 084 058/088 059/092 062/090 064/091 065/090 062/090
1/B 30/K 00/U 00/U 00/B 21/B 21/U
4BQ 083 058/087 058/092 062/090 065/091 065/090 063/089
2/T 50/U 00/U 00/U 02/T 32/T 21/U
BHK 083 054/088 055/092 057/089 057/088 059/090 058/090
0/U 20/K 00/U 00/U 01/N 32/W 21/U
SHR 080 052/085 053/091 057/091 060/091 059/088 056/087
5/T 40/U 00/U 00/U 12/T 22/T 22/T
BYZ WATCHES/WARNINGS/ADVISORIES
MT...NONE.
WY...NONE.
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